We propose to develop a program to assess the role of genetic factors in childhood cancer etiology, and to determine the genetic consequences of childhood cancer and its treatment. Genetic factors will be identified through review of the clinical characteristics and family history of childhood cancer patients at the time of diagnosis and at 5 year intervals. Patients with congenital anomalies will be ascertained for chromosomal studies. The genetic consequences of childhood cancer and its therapy will be assessed by follow-up of long term survivors with respect to reproductive risks and risk of subsequent neoplasms. A major objective is to define the fraction of childhood cancers due to detectable genetic factors, and to determine how those factors interact with mutagenic and carcinogenic treatment-related factors in reproductive risks and subsequent carcinogenesis.